The applicant has previous invented apparatus for the comminution of solid materials, these being the subject of published patent applications WO/2005/092509 and WO/2006/093421. These inventions focus more on the comminution of firm materials such as waste wood and timber into a material commonly referred to as hog fuel, though were also able to be used for a range of other solid materials including demolition waste. The inventions relied on a rotating disk with teeth which basically chipped material as it came into contact therewith.
However, a limitation of the invention was that it worked best with material which did not have a high moisture content and which responding well to a chipping action—e.g. woody and brittle materials. In practice, stringy fibrous materials such as flax could eventually clog the machine, its screening apertures, and/or reduce its operating efficiency. Hence the apparatus worked best with non-fibrous materials which responded well to chopping, breaking, or shattering by impact.
Green waste and municipal waste represent a significant problem world wide. Green waste often comprises a high proportion of leafy and green material interspersed with woody material such as branches. There may also be a significant proportion of stringy and fibrous material. This type of waste can be bulky due to large air voids and pockets arising from the typically varied composition of this waste, and comprises materials of substantially different size—from branches and limbs, through to small individual pieces such as lawn clippings. These issues represent a problem for composting—for efficient composting ideally all the material is of a similar size (and ideally blended), and absent of large air pockets. Hence, some processing of the material is desirable to both reduce bulk and increase composting efficiency. The problem is that prior art apparatus suitable for chipping or comminution woody material is often clogged by moist and non-woody material—this requires a preliminary separation step which adds to the cost of recycling and often requires a larger recycling plant area so as to hold the separated materials. The problem still remains as to how to process the separated, and problematic, materials.
As land becomes scarcer, waste and recycling centres with as small a footprint as possible are desirable. A smaller footprint also allows such centres to be situated in urban and suburban areas—this also reduces the carbon footprint for dealing with the waste as it can significantly reduce the distance that green and garden waste material needs to be transported for recycling.
Accordingly, there is a need for apparatus which can comminute common green waste, ideally without initial separation steps, and which can reduce the overall footprint of a waste or recycling management centre for handling green waste. Apparatus which can comminute green waste to a relatively uniform size to facilitate efficient composting into a valuable recyclable commodity, is also desirable. In terms of sustainability, converting waste material into a valuable usable commodity is both economically and environmentally sound, and can subsidise the operation of municipal (and other) waste management centres.
Similar problems also exist for municipal refuse. While recycling programmes are in place in many regions, typical municipal waste often comprises predominantly moist material of a wide range of compositions. Accordingly, apparatus for comminution municipal waste may need to comminute a bulk material which can contain materials as diverse as: disposable diapers, metal cans, bottles, paper and cardboard, plastic bags and bottles, food waste, and whatever else the average consumer decides to put in their waste. Conventional shredders (such as used for woody materials) quickly clog when processing such material, and may only be able to process municipal waste when it is blended with a larger proportion of other materials (e.g. woody material, etc.). Such a solution is not practical and also combines a potentially valuable commodity (green waste) with waste which is often incinerated or buried.
A significant problem in waste management is bulk. Comminution of waste can provide a number of potential advantages—it is more amenable to screening and separation processes which can isolate recyclable materials. It also produces an easily compactable mass, and in landfill sites the waste breaks down much more quickly than bulk waste (another major issue).
There are limited, if any, options known to the inventor allowing the wide range of materials present in bulk municipal waste to be comminuted by one piece of apparatus. Apparatus suitable for woody and hard materials don't like wet or stringy materials. Apparatus for comminution soft materials general balk or stop in the presence of hard or large materials. Fibrous stringy materials tend to represent a problem for all types of apparatus if present in significant amounts.
Accordingly there is a need for apparatus able to comminute both soft and harder waste materials without discrimination. There is particularly a need for apparatus suitable for comminution general green waste and/or municipal waste without the need for wholesale screening or separation of large amounts of material before it is processed by the comminution apparatus.
Accordingly it is an object of the present invention to consider the foregoing problems and provide apparatus which can process a wide range of waste materials with varying moisture contents and composition.
At the very least, it is an object of the present invention to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.